With respect to the OFDM transmission protocol, a reference signal is transmitted for synchronizing the time domain or frequency domain. For example, the phase reference symbol of terrestrial digital multimedia broadcasting (T-DMB) or the discrete, and continuous pilot frequency patterns of digital video broadcasting—terrestrial and handheld, DVB-T/H) and integrated services digital broadcast—terrestrial (ISDB-T) are employed.
Regarding to a frequency synchronization model, an integral multiple frequency offset (IFO) of the sub-carrier space is estimated to perform the method of coarse frequency synchronization (CFS).
FIG. 1 is schematic block diagram of a conventional coarse frequency synchronization (CFS) mechanism. FIG. 2 is schematic view of conventional steps for estimating unit IFO. FIG. 3 is schematic view of performing a conventional coarse frequency synchronization (CFS) method.
Please refer to FIGS. 1-3. Based on conventional techniques, the correlations corresponding to the IFO candidates (D) are calculated while performing CFS mechanism by using one of phase reference symbol correlated method and channel impulse response method wherein the IFO candidates (D) are estimated as IFO when peak value appears, which is termed as the estimation of unit IFO shown in FIG. 2.
Furthermore, if the estimation of unit IFO is tried once, it will cause the incorrect situation. Thus, in order to reduce the incorrect situation, a continuity check or majority vote method is employed to detect the reliability of the estimation of unit IFO for confirming the estimated IFO candidates (D), which is termed as the CFS method shown in FIG. 3.
The duration of performing the above-mentioned CFS method is determined by the product of unit IFO estimation time and the number of times for reliability check. In other words, according to the maximum variation of crystal oscillator (X-TAL) frequency disturbance in the induced IFO, the search or estimation range of the IFO candidates (D) is configured and the maximum peak is found after retrieving all the search or estimation range. Then, the estimation time is multiplied by the number of times during the reliability check to generate the consumption time.
However, even if the maximum variation of crystal oscillator (X-TAL) frequency disturbance is maximized, most of the variation in the crystal oscillator (X-TAL) frequency disturbance is vary small and most of estimated IFO candidates (D) are statistically gathered near the zero value. Further, when the transmission signal is very weak and the reliability check is still performed, it takes more consumption time during the reliability check.